Liz wants to buy her favorite musical group’s new cd. the cd costs $15.24, including tax. liz gives the store clerk a twenty-dollar bill. how much change should liz get back?

The coverage of a base station of a telecommunication company forms a disk with a radius of (kilometers). let be the distance of a cellphone from a base station. assume that the location of cellphones in use are randomly uniformly distributed within the disk. calculate the mean and variance for the random variable.